Ordinary (monostatic) radar systems have to transmitter and receiver co-located on the same platform. This radar has the disadvantage that the transmitter may be detected from a great distance. If used in a military vehicle or aircraft an enemy may easily determine its location. Bistatic radar was developed wherein the transmitter and receiver are located separately, allowing the vehicle or aircraft to receive only and thus avoid detection by an enemy.
A bistatic radar transmitter may be located on a platform that is difficult for an enemy to destroy, such as on a low earth orbit satellite. At present the timing of the low earth orbit systems are known and the enemy has ceased all operation during the surveillance. In addition, low earth orbit satellite radars require a network of many satellites to provide comprehensive coverage. It is possible to have gaps as large as 15 to 20 minutes, creating a handoff problem from one satellite to the next. Therefore, there is a need for a method for continuous surveillance and quiet attack capability in military situations. In addition, passive continuous surveillance and tracking of targets may be useful in homeland security and in commercial applications.